The present invention relates to a method of producing vinyl chloride-based resins having excellent deformation resistance under heat and processibility into plate, sheet, film, profile articles, pipe, blow molded articles, etc.
Up to this day, improvement in the deformation resistance of poly(vinyl chloride) under heat, has been attempted by post-chlorination of poly(vinyl chloride), or this post-chlorinated poly(vinyl chloride) (hereinafter abbreviated as chlorinated PVC) has been blended with additional poly(vinyl chloride) in any proportions.
Japanese Patent Publications No. Sho 41-9551 or No. Sho 44-12433, show a method of copolymerizing vinyl chloride with N-substituted maleimides.
When using chlorinated PVC for improving the deformation resistance of poly(vinyl chloride) under heat, there are drawbacks such as:
.circle.1 narrow processible latitude when actually processing,
.circle.2 poor thermal stability for processing resulting in remarkable coloration,
.circle.3 large thermal shrinkage at high temperature, and the like.
On the other hand, in the case of copolymers of vinyl chloride with N-substituted maleimides described in Japanese Patent Publication No. Sho 41-9551 or No. Sho 44-12433, such drawbacks as can be seen in chlorinated PVC are improved to some extent. However, new problems have been caused such that the thermal meltability of the PVC is worsened because the N-substituted maleimide, being a rigidity component introduced for raising the deformation resistance under heat, causes a decrease in producibility, coloration is generated in the copolymer during melting due to exposure to high temperature for many hours, and the like.
In order to improve such drawbacks, the type of N-substituted maleimides is restricted in the method described in Japanese Patent Publication No. Sho 44-12433. Furthermore, in order to avoid the peculiar coloration of molded articles made from such copolymers, the polymerization is said to be desirably conducted at a temperature of -10.degree. to 40.degree. C.
This method is however not practical because the particularly restricted N-substituted maleimides have very poor polymerizability further, there are problems in facilities when producing this copolymer industrially.
Moreover, in a method described in Japanese Unexamined Patent Publication No. Sho 61-221209, it is stated that said problems can be improved by allowing a chain transfer agent to coexist and by conducting the polymerization at a temperature lower than 40.degree. C. In this case, too, however, there arise problems such that the polymerizability is poor, and the type of chain transfer agents is restricted to avoid destructive chain transfer, thereby sufficiently improved processibility, and the like, cannot be attained.
The purpose of this invention is to provide a method which is simpler than conventional methods and corresponds closely enough to existing practical producing facilities such that vinyl chloride-based resins having excellent processibility and deformation resistance under heat can be produced without decreasing polymerizability.